Squares and bundles
Owens Corning defines a roofing square as 100 sq ft and says its architectural shingles are packaged three bundles to a square. Its Duration and Supreme product pages list the same 3 bundles per square. Check the packaging of the brand you buy, because a few products are packed differently.
Step 1: roof surface from the footprint
A sloped roof has more surface than the ground it covers. Pitch is written as rise over a 12 inch run, so 6:12 rises 6 inches for every 12 inches across. The surface is longer than the run by sqrt(rise squared + 12 squared) / 12. That is our arithmetic from the Pythagorean theorem, the same factor Owens Corning's guidance applies as a pitch correction.
Factors: 4:12 is 1.054, 6:12 is 1.118, 8:12 is 1.202, 10:12 is 1.302 and 12:12 is 1.414.
Measure the footprint including the overhangs, not the inside of the walls.
Step 2: add waste
Owens Corning recommends 10 to 15 percent extra for waste and trimming. Use the lower figure for a plain gable roof and the higher one for roofs with several hips, valleys or dormers, where more shingles are cut and thrown away.
Worked example
A house footprint of 40 by 30 feet is 1,200 sq ft. At 6:12 the roof surface is 1,200 x 1.118 = 1,342 sq ft. With 10 percent waste that is 1,476 sq ft, or 14.8 squares. At 3 bundles per square that is 44.3, so 45 bundles.
With 15 percent waste for a more complex roof: 1,342 x 1.15 = 1,543 sq ft, 15.4 squares, 46.3 bundles, so 47.
What the bundle count does not include
- Starter strip along the eaves and rakes.
- Ridge and hip cap shingles. Their coverage is given in linear feet per bundle and differs by product; read the packaging.
- Underlayment, ice and water barrier, drip edge, flashing, nails and vents.
- Tear-off and disposal if you are removing an old roof.
Safety and permits
Falls are the main danger in roofing. Use fall protection, work in dry weather, and think hard about whether this is a job for a professional. Many places require a permit for a re-roof and limit how many layers of shingles a roof can carry, so ask your building department before you start.
How many bundles for common house sizes
Each row is the footprint of the roof (the area it covers on the ground, overhangs included) with a simple shape, 10% extra and 3 bundles per square. Change any number in the roofing calculator.
| Roof footprint | 4:12 pitch | 6:12 pitch | 8:12 pitch | 12:12 pitch |
|---|---|---|---|---|
| 1000 sq ft footprint | 35 | 37 | 40 | 47 |
| 1200 sq ft footprint | 42 | 45 | 48 | 57 |
| 1500 sq ft footprint | 53 | 56 | 60 | 71 |
| 1800 sq ft footprint | 63 | 67 | 72 | 85 |
| 2000 sq ft footprint | 70 | 74 | 80 | 94 |
| 2400 sq ft footprint | 84 | 89 | 96 | 113 |
Frequently asked questions
How many bundles of shingles are in a square?
Three for most asphalt shingles, according to Owens Corning's guidance and product pages. A square covers 100 sq ft of roof.
How much extra should I order?
Owens Corning recommends 10 to 15 percent extra for waste and trimming. Order toward 15 percent for roofs with many hips and valleys.
How do I find my roof pitch?
Measure how many inches the roof rises over a 12 inch horizontal run, using a level and tape in the attic or a pitch gauge. The result is written as rise:12, for example 6:12.
Do I need to know the footprint or the roof surface?
Start from the footprint and multiply by the pitch factor. If your roof has several sections at different pitches, calculate each one and add them.
Does this include starter and ridge shingles?
No. Those are bought separately and their coverage differs by product. Check the packaging, and ask your supplier.
Sources: Owens Corning: DIY roofing guide, Owens Corning Duration shingles: packaging. Read 7 November 2026.
What you will also need for roofing shingles
Tools and supplies that go with this job. These are Amazon search links, so you can compare options and current prices there.
- Roofing safety harness kit
- Chalk line
- Roofing hatchet or hammer
- Hook blade utility knife
- Roofing nails
- Work gloves
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